Primer for cured silicone release agents



United States Patent PRIMER FOR 'CURED SILICONE RELEASE AGENTS Hal J. Northrup, Midland, Mich., assignor to Dow Corning Corporation, Midland, Mich, a corporation of Michigan No Drawing. Filed Sept. 29, 1965, Ser. No. 491,414 US. Cl. 260-291 1 Claim Int. Cl. C08g 31/12; C0911 3/82 ABSTRACT OF THE DISCLOSURE A composition useful for coating cellulose substrates with a silicone release agent and a coupling agent is disclosed. The composition is a mixture of a curable organopolysiloxane release agent, a reaction product of where R is a divalent or trivalent organic radical, R is a lower alkyl and R" is a monovalent hydrocarbon radical of no more than 3 carbon atoms and a volatile organic solvent for the curable organopolysiloxane release agent.

This application relates to new adhesion promoters for cured organopolysiloxane release agents on cellulosic substrates.

Cured organopolysiloxane release agents are commercially used on various types of paper and cardboard. An example of such a release agent is a hydroxyl-endblocked dimethylpolysiloxane gum crosslinked with a small amount of methylhydrogenpolysiloxane after application to a cellulosic substrate as shown in US. Patent 3,061,567. EX- amples of other silicone release agents are shown in US. application Ser. No. 477,304, filed Aug. 4, 1965.

The organopolysiloxane release agents have, however, a tendency of being removable from their substrates by abrasion due to a weak bond between the release agent and substrate. A number of primers have been developed to improve the adhesion of the release agents to their substrates including the epoxyacyloxysilanes of US. Patent 3,120,546.

This application relates to a coupling agent for promoting the adhesion of a cured organopolysiloxane release agent to a cellulosic substrate consisting essentially of the reaction product of from 25 to 75 weight percent of:

(a) a silane of the formula or Iu oH-Rsi 0R' and from 25 to 75 weight percent of (b) a silane of the formula R S1 OCUHI! 3 R is a divalent or trivalent radical consisting of carbon and hydrogen, any other atoms present being oxygen in an ether or carboxylic ester linkage,

R is a lower alkyl radical,

n has a value of 1 to 2, and

R" is a monovalent hydrocarbon radical of no more than 3 carbon atoms,

R being trivalent when n has a value of l and divalent when n has a value of 2.

The coupling agents of this invention exhibit superiority over the previously known primers in that they provide ice firm coupling of the silicone release agent to its cellulosic substrate without significantly altering the release properties of the agent, and, additionally, the primer can be added to a solvent solution of the silicone release agent to provide one-step application of primer and release agent, while lengthening the time which elapses before gelation of the release agent occurs in the bath. The previously-known primers fail to consistently yield all of the above advantages, as compared with the primers of this invention.

R can be any radical as defined above, e.g. methylene, ethylene, propylene, butylene, decylene, phenylene, xenylene, cyclohexylene, cyclopentylene, methylcyclohexylene, tolylene and CH CH=CHCH R can also be any divalent ether radical such as O A CH2CH S1(OCH3)2 and 0 ll CHzCHCHzC 0 (IHICHZSMO CH CH3 Examples of ingredient (b) are i CHgSKO C0113):

H II CH3CH2S1(OCCH3)3, and (CH OiCHSKOCCHx):

Ingredients (a) and (b) spontaneously react with each other to form the reaction product of this invention. The reaction takes about 20 days at room temperature, about 2 hours at C., and about 1 hour at 200 C. An unreacted mixture of (a) and (b) does not yield the abovementioned advantages to the same degree as does their reaction product. The presence of the reaction product can therefore be ascertained by observing a marked improvement in the properties of the composition as a primer for a release agent over a mixture of the separate ingredients.

It should be noted that ingredient (b) is operative alone as a primer for release agents, but several times the amount of (b) alone is required to duplicate the adhesion provided by a given amount of the reaction product of (a) and (b). Furthermore, ingredient (b) alone 3 has a tendency of shortening the gel time of a solution of silicone release agent.

Ingredient (a) alone imparts only a minor improvement in the adhesion of silicone release agents to cellulosic substrates.

The epoxyacyloxysilanes mentioned above give irreproducible and varying results as primers for silicone release agents.

The exact chemical nature of the reaction product of this invention is unknown. It has been observed, however, that most of the epoxy groups of ingredient (a) disappear on formation of the reaction product, while a majority of the acetoxy groups of ingredient (b) are retained. The reaction product would therefore appear to contain some sort of an organic polymer with silyl' pendant groups.

A preferred ingredient (a) is a silane of the formula The coupling agents of this invention are generally added to the organopolysiloxane release agent, which is usually dispersed in a volatile solvent such as xylene, perchloroethylene, benzene, octane, cyclohexane, dibutylketone, or dibutylether. This solution, which may also contain a suitable known curing catalyst for the organopolysiloxane release agent, is then applied to the cellulosic substrate and cured after the solvent has evaporated. Examples of suitable curing catalysts are stannous octoate, dibutyltin dilaurate, and tetrabutyl titanate.

Generally, no modifications of the normal techniques for the application and curing of silicone release agents are required when the coupling agents of this invention are used.

A desirable bath for coating a cellulose substrate with a silicone release agent and the coupling agent of this invention consists essentially of (1) 100 parts by weight of a curable organopolysiloxane release agent, (2) from 0.5 to 10 parts by weight of the reaction product of from 25 to 75 weight percent of a silane of the formula and from 25 to 75 weight percent of (b) a silane of the formula where R is a divalent or trivalent radical consisting of carbon and hydrogen, any other atoms present being oxygen in an ether or carboxylic ester linkage, R is a lower alkyl radical, n has a value of 1 to 2, and R" is a monovalent hydrocarbon radical of no more than 3 carbon atoms, R being trivalent when n has a value of 1 and divalent when n has a value of 2, and (3) from 50 to 20,000 parts by weight of a volatile solvent for (1).

The following examples are illustrative only and should not be construed as limiting the invention, which is properly delineated in the appended claim.

EXAMPLE 1 To several samples consisting of about 29 parts by weight of a hydroxyl-endblocked dimethylpolysiloxane having a viscosity at 25 C. of about 8,000 cs., 1 part of a composition of the formula 3 (CH );Si S'iO Si(CH;);

270 parts of Xylene, and a small amount of dibutyltin dilaurate as a curing catalyst, there was added a coupling agent of the type and amount shown below.

The resulting solution was coated on glassine paper with a No. 14 Mayer rod, and cured for 2 minutes at 250 F.

The product was a paper which was coated with a thin film of cured, elastomeric silicone which exhibited excellent release properties. This silicone film was vigorously rubbed with the finger to see whether it would rub off of the paper. The results were as follows:

Coupling agent Rub-off (a) 0.75 part each of vinyltriacetoxysilane and None.

C Elk HO H10 (0 Hz);Sl( 0 0 H03, previously heated together for 16 hours at 250 F.

(b) 0.75 part each of ethyltriacetoxysllane and CHzCHCHaO (CHz)3Sl(O CH3)! previously heated together for 16 hours at 250 F. (c) 0.75 part each of methyltriacetoxysilane and O HEHCHZO (CH1)3Si(O (EH93, previously heated together for 16 hours at 25 (d) 0.14 part of vinyltriaeetoxysilane and 0.40 part oi CHZETHCHzO (CH7);Si(O CHa)a, heated 4 hours at 175 F. and 1 hour at 250 F.

(e) 0.40 part of vinyltriacetoxysilane and 0.14 part of O Hm HO H10 (CH2)sSl(O CHM, heated 4 hours at 175 F. and 1 hour at 250 F. (0 similar to (a), but without prior heating Ve slight. (g) 0.75 part of methyltriacetoxysilane Slight.

O (h) 0.75 part of CH2 HC 1110 (C H2);Si(0 CH2): Considerable.

EXAMPLE 2 When the following amounts of the following coupling agents are added to mixtures of g. of

CH; OH; HO S iO H, 4g. Of (CH SiO S iO Si(CH 3H3 ML SiO L l 2:

1 g. of dibutyltin diacetate as a curing catalyst, and 200 g. of 1,1,1-trichloroethylene, solutions are formed which, when coated on paper and cured at 300 F. for 2 minutes, impart flexible coatings to the paper which are nonadherent to synthetic, nonsilicone adhesives, yet which have excellent adhesion to the paper:

Amount Coupling Agent (a) 1 g Equal weights of isopropyltriacetoxysllane and O E CH: HCHzCHziJHCHzSKO C HDt, heated tor2hours at 4 F. (b) 7 g 4 g. of n-propyltrlacetoxysilaue and 3 g. of

H H10 0 0 H1O H1Si(O C3H1)i, heated for 1 hour a (c) 3 g Equal weights of ethynyltriacetoxysilane and Amount Coupling Agent hours at 150 F.

C Hz? HG HzSi(O C H203, heated for 24 om-orr-rcsnom,

and from 25 to 75 weight percent of (b) a silane of the formula II RSi(0 0 CH9; where:

R is a divalent or trivalent radical consisting of carbon and hydrogen, any other atoms present being oxygen in an ether or carboxylic ester linkage,

R is a lower alkyl radical,

n has a value of 1 to 2, and

R" is a monovalent hydrocarbon radical of no more than 3 carbon atoms,

R being trivalent when n has a value of 1 and divalent when n has a value of 2,

wherein most of the epoxy groups of (a) disappear on formation of the reaction product and a majority of the acetoxy groups of ingredient (b) are retained, and

(3) from 50 to 20,000 parts by weight of a volatile organic solvent for (1).

References Cited UNITED STATES PATENTS 3,169,884 2/1965 Marzocchi et a1. 117-124 3,076,726 2/1963 Ault et a1 117124 2,946,701 7/1960 Plyeddemann 260-4482 MORRIS LIEBMAN, Primary Examiner.

J. E. CALLAGHAN, Assistant Examiner.

US. Cl. X.R. 

